Effects of catharanthus roseus and centella asiatica leaf extracts on enzymes of glutamine catabolism in human colon carcinoma (CACO-2) cell line and in enterocytes from male sprague-dawley rats.

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Phosphate-dependent glutaminase (PDG) is a key enzyme in several physiological processes and hence has become a target of anti-cancer drug development because of the role of glutamine in providing energy for rapidly dividing cells. This study investigated the effects of the Centella asiatica and Catharanthus roseus leaf extracts on enzymes of glutamine catabolism in human colon carcinoma (Caco-2) cell line and in enterocytes from Sprague-Dawely rats both treated with plant extracts. Our hypothesis was that these extracts would arrest the growth of Caco-2 cells by inhibiting glutaminase but have less deleterious effects on normal cells due to the former being more avid consumers of glutamine. The 3-(4, 5-Dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) assay was used to assess the cytotoxic effects, and hence the anti-cancer potential of extracts from medicinal plants C. asiatica and C. roseus against Caco-2 and human embryonic kidney (HEK 293) cell lines. These in vitro effects were assessed using various doses of plant extracts (0- 16 mg/ml) and different exposure periods of 24, 48 and 72 h. Results show that the cytotoxicity effect of the C. asiatica extract to the caco-2 cell line is dose dependent whilst C. roseus treatment decreased the Caco-2 cells viability at all the exposure times but this was not dose-dependent. In contrast, both extracts significantly increased cell proliferation of the HEK 293 cells compared to the controls. The PDG and ALT activities were decreased in Caco-2 cells whilst the HEK293 cells were largely unaffected. In the in vivo studies, the activities of phosphate-dependent glutaminase (PDG), glutamate dehydrogenase (GDH), aspartate aminotransferase (AST) and alanine aminotransferase (ALT) were determined in the enterocytes. Results show that the activities of GDH remained constant whilst there was a decrease in ALT and a slight increase in AST activities in the enterocytes in both the C. asiatica and C. roseus treated groups. The PDG enterocytes activity, on the other hand, was lower in both the treated groups compared to the control group. Expression of both PDG and AST assessed by dot blots in the enterocytes increased in both plant extract treated groups. Induction of apoptosis was also investigated using cytochrome c. The plant extracts were screened for presence of phytocomponents that may be causing changes in Caco-2 cell growth and in enzymes of glutamine catabolism using Gas Chromatography-Mass Spectrometry (GC-MS) and qualitative phytochemical analysis. The extracts revealed the presence of anticancer and many other compounds. We conclude that the both extracts have potent anti-cancer cell activity that leaves normal cells unaffected, in fact stimulating their growth.